This invention relates to a power source system including a harmonic or damped filter for attenuating harmonic current generated on an AC bus and a power regenerating circuit adding fundamental and harmonic components of power generated by the action of the harmonic filter to the DC output circuit in a converter.
It has been well known in the art that harmonic current is generated on an AC bus, to which a cycloconverter, converter or the like is connected. This harmonic current has an adverse effects upon various power apparatus. For example, overloading or overheating of an apparatus due to harmonic current or the distorted voltage caused by a harmonic component is likely to occur.
It has been in practice to attenuate or suppress such harmonic current by connecting a harmonic filter on the AC bus. The harmonic filter usually consists of a combination of four tuned filters for attenuating respective 5th, 7th, 11th and 13th harmonics and a highpass filter for attenuating higher harmonics. The harmonic filter used to this end is not only bulky by itself but also requires a cooling equipment for its reactor and resistor. For example, when such a harmonic filter is employed in an HVDC power link, the required space amounts to more than 50% of that of the entire converter station.
A highpass filter has been used as damping filter whose characteristic frequency is generally chosen at a high harmonic order. Reduction of the above frequency leads to increase in a filter loss at fundamental frequency which is given as follows, concerning a conventional highpass filter. EQU I.sup.2 R=(Q.sub.sc /N.sub.r.sup.3)Q
where
Q.sub.sc : reactive power rating PA1 Q: quality factor PA1 N.sub.r : harmonic order
For example, under the condition N.sub.r =4 and Q=1.0, the above filter loss amounts to as high as about 1.6% of the filter capacity. This means that filter rating Q.sub.sc =50 MVar will produce a filter loss 800 KW. This is not practical for actual system in view of saving energy as well as requiring a large size cooling equipment.